Liftable axles, such as tag or pusher axles, may be provided on vehicles, including truck tractors, such as, for example, dump trucks or cement mixers. When the vehicle is deployed, such liftable axles assist in transferring the vehicle load to the ground. When the vehicle is unloaded, such liftable axles may be lifted off the ground, to prevent undue tire wear and improve fuel economy.
Tag or pusher liftable axles present a number of problems, due to the fact they typically are self-steering and liftable, including limiting the vehicle speed and articulations of the vehicle or the tag or pusher axle, when the axle is lowered. Such axles also typically present increased wheel wobble and tire wear, reduced roll rate, reduced lateral stiffness, unequal load distribution, and reduced agility, especially on rough terrain. Furthermore, such axles experience additional bending loads due to lateral and breaking loads, which necessitate the use of very robust and heavy liftable axles, which further reduce fuel economy and occupy valuable vehicle space.
The present invention is directed towards an improved suspension system for a self-steering liftable axle.